TOKYO (AFP) - Japan's ANA is to test one of its modified Dreamliner jets on Sunday, three months after the worldwide fleet of 787s was grounded, as Boeing seeks to reassure passengers that the planes are safe.

All Nippon Airways has the world's largest fleet of the next-generation planes and Sunday's flight will have the company's chief and Boeing's CEO on board, with both of them anxious to put the damaging crisis behind them.

The US Federal Aviation Administration and other regulators grounded the worldwide Dreamliner fleet in mid-January after failures of the lithium-ion batteries on the jetliner caused a fire on board one parked plane in Boston and forced the emergency landing of an ANA-operated plane in Japan.

Following months of investigations, the FAA on Thursday issued formal approval of Boeing's battery fix, with Ethiopian Airlines on Saturday becoming the first carrier to resume using the aircraft in a flight from Addis Ababa to Nairobi.

Speaking in Tokyo on Saturday, Mike Sinnett, Boeing's chief project manager for the Dreamliner programme said the Japanese test flight showed the faith that the US aircraft manufacturer placed in the battery fix.

"What it represents is... the depth of confidence that (Boeing CEO) Ray Conner has in the series of design solutions we have brought forward," Sinnett told reporters.

The test flight Sunday morning, to and from Tokyo's Haneda airport, will also have ANA Chairman Shinichiro Ito on board, according to the airline, which already has 17 Dreamliners and dozens more on order.

ANA and domestic rival Japan Airlines (JAL) account for around half the 50 Dreamliners in service worldwide, but it could still be at least a month before they can complete all the battery fixes and get their planes in the air.

Although the exact cause of the battery failures had yet to be pinpointed - as noted by the FAA on Thursday - Sinnett insisted that the refitted planes were safe to fly.

"Even if we missed the root cause, we have identified 80 potential causal factors and we have addressed all of them in the design," he said.

The battery solution eliminated the potential for fire and heat to get into the airplane, he said.